The present invention relates to a masterslice integrated circuit device. More particularly, it relates to a semiconductor device having a large number of input/output buffers and a logic gate array and to a method for manufacturing the same by using masterslice technology.

In general, in a large-scale integrated (LSI) semiconductor circuit of complex logic, customers may request a preferred design. Therefore, when designers design logic LSI layout patterns in accordance with the customers' requirements, the design time becomes remarkably long, and, therefore, the manufacturing cost of logic LSI semiconductor circuits becomes high.

Therefore, for logic LSIs, it is essential to use a standard layout pattern so as to shorten the design time and lower the manufacturing cost. Several approaches have been taken to meet this requirement. One approach is masterslice (gate array) technology in which a standard layout pattern mainly for active areas and a custom-made layout pattern mainly for interconnections are prepared and merged into mask patterns for designing masks.

On the other hand, in an internal circuit of a logic LSI semiconductor device, a signal is transmitted by a small driving power and a small signal amplitude to enhance the operation speed. However, when a signal is transmitted from the internal circuit of the logic LSI semiconductor device to an external circuit outside the logic LSI semiconductor device, a large driving power is necessary. In addition, when there is a difference in the signal level between the internal circuit and the external circuit, level conversion is also necessary. For this purpose, a large number of input output buffers are provided on the perimeter of the logic LSI semiconductor device. Of course, such buffers are also manufactured by using masterslice technology.

In a prior art method for a semiconductor device having a large number of buffers, a plurality of buffer patterns are prepared as a standard layout pattern. In this case, each buffer pattern has a definite number of inputs and a definite number of outputs. For example, each buffer pattern has three inputs and one output. Next, a custom-made layout pattern is prepared for interconnections between the internal circuit and the inputs of each buffer.

In the above-mentioned prior art, however, since each buffer pattern has a definite number of inputs, the number of connection configurations between the internal circuit and the buffers is limited.

It is desirable to provide a masterslice integrated circuit device having a large number of input/output buffers and to provide a method for manufacturing the same by using masterslice technology in which the number of connection configurations between the internal circuit and the buffers is increased.

According to one aspect of the present invention, there is provided a masterslice integrated circuit device including a plurality of input and output logic gates disposed in a peripheral region thereof, a plurality of internal logic gates disposed in a central region thereof, and a custom-made wiring pattern disposed between the logic gates to desired function, the logic gates being arranged in the form of an array, at least one of the logic gates comprising: a plurality of PNP transistors each of the PNP transistors having a base for receiving a first signal and an emitter for providing a second signal corresponding to the first signal; and a plurality of output stage circuits which are arranged at positions so that at least one of the PNP transistors can be connected to one of the output stage circuits by the custom-made wiring pattern, one of the output stage circuits being connected to the emitter of at least one of the plurality of PNP transistors to form one of the logic gates.

According to a second aspect of the present invention, there is provided a method for manufacturing a masterslice integrated circuit device including a plurality of input and output logic gates disposed in a peripheral region thereof, a plurality of internal logic gates disposed in a central region thereof, and a custom-made wiring pattern disposed between the logic gates to desired function, the logic gates being arranged in the form of an array, the method comprising the steps of: forming a plurality of PNP transistors, each of the PNP transistors having a base for receiving a first signal and an emitter for providing a second signal corresponding to the first signal; forming a plurality of output stage circuits at positions so that at least one of the PNP transistors can be connected to one of the output stage circuits, each of the plurality of output stage circuits having an input and an output terminals; and electrically connecting the emitter of at least one of the plurality of PNP transistors to the input terminal of one of the plurality of output stage circuits to form one of the logic gates.

Reference will now be made, by way of example to the accompanying drawings, wherein

• Fig. 1 is an equivalent circuit diagram illustrating a prior art masterslice integrated circuit device manufactured by using masterslice technology;
• Fig. 2 is a logic circuit diagram of the circuit of Fig. 1;
• Fig. 3 is an equivalent circuit diagram illustrating an embodiment of a masterslice integrated circuit device embodying the present invention;
• Figs. 4A through 4D are logic circuit diagrams of the circuit of Fig. 3;
• Fig. 5 is a circuit diagram in which the circuit of Fig. 1 is used as an output buffer of a logic LSI gate array;
• Fig. 6 is a circuit diagram in which the circuit of Fig. 3 is used as an output buffer of a logic LSI gate array;
• Figs. 7A and 7B are cross-sectional views illustrating NPN and PNP transistors; and
• Fig. 8 is a plane view of an output buffer of Fig. 4A.

In Fig. 1, G_A and G_B designate buffer patterns constructed as transistor-transistor logic (TTL) patterns. Each buffer pattern G_A and G_e comprises resistors R₁ through R₄, transistors Q₁ through Q₄, and a diode D₁ to form a three-input NAND circuit. The transistor Q₁ is a multiemitter transistor having three emitters. The transistor Q₂ serves as an inverter. The transistors Q₃ and Q₄ form an output stage. That is, when one of the transistors Q₃ and Q₄ is turned on, the other is turned off.

The standard layout pattern represented by the buffer patterns G_A and G_B is connected to an internal circuit (not shown) by a custom-made layout pattern for interconnections. That is, inputs I₁, I₂, ..., I₆of the buffer patterns G_A and G_B are connected selectively to logic gates of the internal circuit.

Note that, generally, in a masterslice integrated circuit device, a plurality of such input and output buffers which are also logic gates are arranged in a peripheral region, while a plurality of such internal logic gates are arranged in a central region. In addition, both types of the logic gates are arranged in the form of an array.

In the buffer pattern G_A, when at least one of the inputs 1₁, I₂, and 1₃ is at a low potential, a current flows from the power supply V_cc through the resistor R₁ and the base and emitter of the transistor Q₁ to the internal circuit. As a result, the transistor Q₂ is turned off, and, accordingly, the transistors Q₃ and Q₄ are turned off and on, respectively, so as to cause the output O_A to be at a high potential. Contrary to this, when all the inputs I₁ through 1₃ are at a high potential, a current flows from the power supply V_cc through the base and collector of the transistor Q₁ to the base of the transistor Q₂. As a result, the transistor Q₂ is turned on, and, accordingly, the transistors Q₃ and Q₄ are turned off and on, respectively, so as to cause the output O_A to be at a low potential.

In Fig. 1, however, since the buffer pattern G_A or G_B has a definite number of inputs, such as three inputs, the number of connection configurations between the internal circuit and the inputs of the buffers is limited. For example, as illustrated in Fig. 2, which is a logic circuit of the buffer patterns G_A and G_B of Fig. 1, each of the inputs I_{1 through} I₆ is connected to one logic gate of the internal circuit (not shown). In addition, if only one logic gate of the internal circuit is connected to the buffer pattern G_A by a custom-made layout pattern, only one input, such as the input 1₁, is used while the other inputs 1₂ and 1₃ are unused. Therefore, wasted areas are created. Further, if four logic gates of the internal circuit are connected to the buffer pattern G_A by a custom-made layout pattern, another kind of transistor Q₁ must be prepared and must be connected by the custom-made layout pattern to the buffer pattern G_A, and this procedure becomes complex.

In Fig. 3, which illustrates an embodiment of the present invention, as a standard layout pattern for buffers which are, in this case, output buffers, two kinds of patterns are prepared. That is, a plurality of input stage patterns IS₁, IS2, ..., IS₅ are regularly arranged and a plurality of output stage patterns OS_A and OS_B are regularly arranged. The input stage patterns are connected by a custom-made layout pattern (not shown) to the output stage patterns OS_A and OS_B so as to form output buffers.

Each input stage pattern, such as the IS₁, comprises a PNP transistor Q₁₁ having a base for an input 1₁, an emitter for an output, and a grounded collector. On the other hand, each output stage pattern, such as the OS_A, comprises NPN transistors Q₂, Q₃, and Q₄, resistors R₁, R₂, R₃, and R₄, and a diode D₁. That is, the PNP transistors Q₁₁ through Q,₅ correspond to the transistor Q₁ of Fig. 1.

Note that in Fig. 1 the transistors are all of the NPN type while in Fig. 3 each input stage pattern comprises a PNP transistor and each output stage pattern comprises NPN transistors.

A custom-made layout pattern is provided to selectively connect the emitters E₁ through E₅ of the input stage patterns to the bases B_A and B_B of the output stage patterns. Various configurations of the buffers G_A' and G_B' are realized. For example, when the emitter E₁ is connected to the base B_A while the emitters E₂ through E₅ are connected to the base B_B, the buffer G_A' serves as an inverter while the gate G_B' serves as a four- input NAND circuit, as illustrated in Fig. 4A. When the emitters E₁ and E₂ are connected to the base B_A while the emitters E₃, E₄, and E₅ are connected to the base B_B, the gate G_A' serves as a two-input NAND circuit while the gate G_B' serves as a three-input NAND circuit, as illustrated in Fig. 4B. When the emitters E₁, E₂, and E₃ are connected to the base B_A while the emitters E₄ and E₅ are connected to the base B_B, the gate G_A' serves as a three-input NAND circuit while the gate G_B' serves as a two-input NAND circuit, as illustrated in Fig. 4C. When the emitters E₁ through E₄ are connected to the base B_A while the emitter E₅ is connected to the base B_B, the gate G_A' serves as a two-input NAND circuit while the gate G_B' serves as an inverter, as illustrated in Fig. 4D. The number of configurations of the buffers G_A' and G_B' is increased by increasing the number of input stage patterns or PNP transistors.

Thus, in an embodiment of the present invention, it is possible to increase the degree of freedom regarding the number of inputs as compared with some prior devices.

In the circuit of Fig. 3, when the emitters E₁ and E₂ of the transistors Q₁₁ and Q₁₂ are connected to the base B_A of the transistor Q₂ of the output stage pattern OS_A, a two-input NAND circuit G_A' is realized, as illustrated in Fig. 4B. Therefore, when at least one of the inputs I₁ and 1₂ is at a low potential, the output O_A is at a high potential. That is, when the input I₁ is at a low potential, the transistor Q₁₁ is turned on. As a result, most of the current flowing through the resistor R₁ flows into the emitter and collector of the transistor Q₁₁, and, accordingly, the transistor Q₂ is turned off so as to turn on the transistor Q₃ and turn off the transistor Q₄. Therefore, the output O_A is at a high potential. On the other hand, when both of the inputs I₁ and 1₂ are at a high potential, the transistors Q₁₁ and Q₁₂ are turned off so that most of the current flowing through the resistor R₁ flows into the base emitter of the transistor Q₂. Accordingly, the transistor Q₂ is turned on so as to turn off the transistor Q₃ and turn on the transistor Q₄. Therefore, the output O_A is at a low potential and thus NAND logic operation is performed.

When the input 1₁ is at a low potential, the base current flowing through the emitter base of the transistor Q₁₁ is 1/h_FE of the collector current flowing through the emitter and collector of the transistor Q₁₁. Therefore, this base current is very small, which means that the driving power of the internal circuit of the NAND circuit G_A' can be small. That is, the fan-out (the number of outputs) of the internal circuit can be increased.

In Fig. 3, even if all the transistors Q₁₁ through Q₁₅ are replaced by diodes, various configurations of buffers as illustrated in Figs. 4A through 4D can be obtained by a custom-made layout pattern. In this case, however, when an input or a cathode of one diode is at a low potential, the current flowing through the resistor R₁ flows through the diode into the internal circuit, thereby decreasing the fan-out, or the number of outputs of the internal circuit.

In Fig. 3, if Q₁₁ through Q₁₅ are NPN transistors formed in individual isolated regions of a semiconductor device and each NPN transistor has a collector selectively connected to the base B_A or the base B_B, a base for an input, and a grounded emitter, the buffers G_A' and G_B' serve as OR circuits, not as NAND circuits. If such individual NPN transistors are used for a NAND logic, it is necessary that the base of each transistor be connected by a connection to the resistor R₁ and that the collector of each transistor be connected by a connection to the base B_A. As a result, the connections become complex, and, in addition, the collector capacity can become large. Contrary to this, in embodiments of the invention, the collector of each PNP transistor is commonly grounded, and therefore the collector capacity can be kept small.

In Fig. 5, the buffer pattern G_A of Fig. 1 is connected to an internal logic gate IG of an internal circuit. The logic gate IG is also constructed as a TTL circuit comprising transistors Q₂, and Q₂₂, resistors R₅, R₆, R₇, and R_e, and a diode D₂. In this case, the diode D₂ and the resistor R₈ form a clamp circuit for clamping the high level of the output voltage V_o.

In the buffer pattern G_A, the threshold voltage V_th of the input 1₁ is represented by:where V_sc is the base to collector voltage of the transistor Q₁; V_BE1 is the base to emitter voltage of the transistor Q₂; V_BE2 is the base to emitter voltage of the transistor Q₄; and V_BE3 is the base to emitter voltage of the transistor Q₁. If it is assumed that V_BE1≅V_BE2≅V_BE3 V_BE≅0.8V and V_BE3-VBC≅0.1 V, thenIn addition, the low-level of the output 0_A equals the collector-emitter voltage V_CE of the transistor Q₄, that is, about 0.1V, while the high-level of the output O_A equals V_CC-2V_BE, that is, about 3.5V, when V_cc=5V.

On the other hand, in the internal logic gate IG, the threshold voltage V_th is represented by

• V_th=V_BC+V_BE1-V_BE2

In Fig. 5, in order to match the buffer pattern G_A to the internal logic gate IG, the high-level of the output V_o of the gate IG should be higher than the threshold voltage V_th (=1.5V) of the buffer pattern G_A. Therefore, it is desirable to enlarge the amplitude of the output V_o by cutting the clamp circuit away, which can be disadvantageous in respect to operation speed.

In Fig. 6, the buffer pattern G_A' of Fig. 3 is connected to the internal logic gate IG. In the buffer pattern G_A', the threshold voltage V_th of the input I, is represented by:where V_BE1 is the base to emitter voltage of the transistor Q₂, V_BE2 is the base to emitter voltage of the transistor Q₄, and V_BE3 is the base to emitter voltage of the transistor Q₁₁. If it is assumed thatthen V_th≅V_BE≅0.8V, which is half of the threshold voltage of the prior art.

In the internal logic gate IG, the high-level of the output V_o is clamped by a series circuit of the two diodes D₂ and D₃ at about 1.5V since the forward voltage of each diode is equal to or smaller than 0.8V. Therefore, the swing or amplitude of the output V_o is about 0.1 to 1.5V. In addition, when one of the diodes D₂ and D₃ is constructed as a Schottky barrier diode, the amplitude of the output V_o is about 0.1 to 1.2V. In this case, the threshold voltage of the buffer pattern G_A' is approximately an intermediate value of the amplitude of the output V_a, which voltage reasonably drives the buffer pattern G_A'.

In a structure embodying the present invention, there are two kinds of transistors, that is, NPN transistors and PNP transistors. Such two kinds of transistors are formed in a semiconductor device. For example, in Figs. 7A and 7B, reference numeral 71 designates a semiconductor substrate lightly doped with N-type impurities. An N^+-type buried layer 72 having a high concentration is formed on the substrate 71, and, in addition, an N-type epitaxial layer 73 is deposited thereon. Within the epitaxial layer 73 are formed a P^+-type impurity diffusion layer 74, a P^+-type impurity diffusion layer 75, an N^+-type impurity diffusion layer 76, and an N^+-type impurity diffusion layer 77. In Fig. 7A, the layers 77, 75, and 73 are an emitter region, a base region, and a collector region, respectively, of an NPN transistor while in Fig. 7B, the layers 75 and 73 and the substrate 71 are an emitter region, a base region, and a collector region, respectively of a PNP transistor. Note that the collector region of the PNP transistor of Fig. 7B can be commonly grounded by grounding the substrate 71. In addition, in Fig. 7B, the buried layer 72 is small; however, the buried layer 72 can be omitted. Further, in Fig. 7B, the base width is large so that the value h_FE is small; however, such a small value h_FE is sufficient for a buffer.

In the circuit of Fig. 8, a custom-made layout pattern (interconnections) is illustrated by the shaded portions. the circuit of Fig. 8 corresponds to that of Fig. 4A.

In embodiments of the present invention, since the input stage of a buffer is constructed as single-emitter PNP transistors which are prepared without connections, the input stage of each buffer is voluntarily altered by a custom-made layout pattern and thereby the buffer can be better utilized. In addition, the input threshold voltage of each buffer can be small, and therefore suitable for a high speed LSI semiconductor circuit having a small amplitude.